Optical Sensor Synchronization for Film Thickness Monitoring
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Solution Overview
Problem
Traditional substrate processing systems face challenges in accurately monitoring and controlling film thickness, critical dimension targeting, and line roughness due to interference effects from multiple wavelengths during photolithography processes, especially as geometries shrink, leading to increased technical difficulties in forming structures on substrates.
Innovation Solution
The implementation of optical sensors, such as cameras or spectrometers, that utilize specific wavelengths, optimized light sources, and filtering techniques to minimize interference effects, along with synchronization of the optical sensor's frame rate with the substrate's rotational speed, to improve film thickness measurement capabilities and reduce signal noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple wavelengths are used in photolithography processes, then the processing capability is enhanced, but interference effects increase leading to reduced measurement precision
Solution Approach 1:
The patent extracts and analyzes reflected light at specific wavelengths from the multi-wavelength photolithography process. By using optical sensors to detect reflected light at predetermined wavelengths and analyzing the spectral characteristics, the system isolates the interference patterns caused by film thickness from the complex multi-wavelength environment, enabling precise measurement despite the presence of multiple wavelengths in the processing system.
Solution Approach 2:
The patent changes the parameter of wavelength selection by using optical sensors to detect reflected light at specific predetermined wavelengths rather than analyzing the full spectrum. By monitoring reflectivity at selected wavelengths and using Fourier transform analysis, the system converts the complex multi-wavelength interference into measurable parameters that directly correlate with film thickness, resolving the measurement precision issue.
2Measurement precision
If optical sensors are used to monitor film thickness, then measurement capability is improved, but signal noise increases due to interference from multiple wavelengths
Solution Approach 1:
The patent introduces Fourier transform analysis as an intermediary processing step between the optical sensor detection and the film thickness calculation. The Fourier transform converts the time-domain reflected light intensity signals into frequency-domain spectra, allowing the system to identify and extract the specific frequency components corresponding to film thickness interference patterns while filtering out noise from other sources including other wavelengths.
Solution Approach 2:
The patent transforms the measurement parameter from direct intensity measurement to spectral frequency analysis. By applying Fourier transform to the reflected light signals and analyzing the frequency spectrum, the system converts noisy time-domain signals into clean frequency-domain representations where the film thickness information appears as distinct peaks, effectively separating signal from noise.
3Productivity
If the optical sensor frame rate is increased to capture faster substrate rotation, then measurement speed is improved, but synchronization difficulty increases
Solution Approach 1:
The patent implements a feedback control system where the substrate rotation speed is monitored and the optical sensor frame rate is adjusted accordingly. The system uses the known rotation speed as feedback to determine the optimal sampling rate, ensuring that measurements are taken at consistent phases of substrate rotation. This feedback mechanism simplifies synchronization by using the rotation speed itself as the reference for timing the optical measurements.
Solution Approach 2:
The patent employs periodic sampling synchronized with the substrate rotation period. By capturing optical measurements at regular intervals that correspond to the substrate rotation cycle, the system ensures that each measurement is taken at the same rotational phase, eliminating the need for complex continuous synchronization while maintaining measurement accuracy at high speeds.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances the accuracy of film thickness measurement and reduces signal noise, providing improved monitoring and control of the fluid dispense process, thereby addressing the challenges of interference effects and ensuring precise substrate processing.
Implementation Method 1
obtaining spectral data, for a given wavelength or range of wavelengths, from a substrate
Implementation Method 2
interference effects from multiple wavelengths during photolithography processes
Data Source
AI summary
Embodiments of systems and methods for monitoring one or more characteristics of a substrate are disclosed. Various embodiments of utilizing optical sensors (in one embodiment a camera) to provide data regarding characteristics of a fluid dispensed upon the substrate are described. A variety of hardware improvements and methods are provided to improve the collection and analysis of the sensor data. More specifically, a wide variety of hardware related techniques may be utilized, either in combination or singularly, to improve the collection of data using the optical sensor. These hardware techniques may include improvements to the light source, improvements to the optical sensors, the relationship of the physical orientation of the light source to the optical sensor, the selection of certain pixels of the image for analysis, and the relationship of the optical sensor frame rate with the rotational speed of the substrate.